There is growing interest to use hydrogen as a transportation fuel in cars, buses, trucks, and other vehicles. Hydrogen is generally stored in a fuel tank on-board the vehicles at high pressure. After most of the on-board hydrogen has been depleted, the pressure of the hydrogen in the fuel tank is reduced and the fuel tank must be refueled with hydrogen.
During refueling, hydrogen is dispensed into the fuel tank at a hydrogen dispensing station. The dispensing station includes a hydrogen supply, which can be one or more high pressure storage tanks. Hydrogen is transferred from the high pressure storage tank into the fuel tank. The driving force for transferring hydrogen is the pressure difference between the high pressure storage tank and the vehicle fuel tank.
The transfer line between the high pressure storage tank and the fuel tank typically includes block and bleed valves. A block valve blocks the flow from the high pressure storage tank and a bleed valve allows a portion of the hydrogen trapped between the block valve and the dispensing nozzle to discharge, thereby reducing the pressure at the dispensing nozzle. Accepted standards, such as SAE J2600 and ISO 17268, require that the pressure at the nozzle be less than 0.5 MPa (gauge) before the dispensing nozzle can be disconnected from the fueling receptacle on the vehicle.
While the transfer line between the block valve and the dispensing nozzle will be at a lower pressure after dispensing hydrogen to a vehicle, the residual hydrogen trapped in the transfer line between the control valve and the block valve will still be at high pressure.
When the next vehicle is connected for refueling, the block valve opens and the high pressure residual hydrogen rushes into the fuel tank. The fast transfer of the residual high pressure hydrogen into the fuel tank causes an undesirable pressure spike in the vehicle fuel system, a pressure spike that can be as high as 20 MPa. This pressure spike is associated with flow rates greater than 60 g/s, which is a flow rate limit defined by various component manufacturers. Exceeding this flow rate limit may lead to damage, for example, component erosion, check valve damage, and filter damage.
Industry desires to limit pressure spikes during hydrogen dispensing.